Thanks to advances in medicine, bone marrow transplants are no longer the last resorts they once were. Every year, thousands of marrow transplants are performed, a common treatment for ailments from bone marrow disease to leukemia. But because they first require a patient undergo radiation to kill off any existing bone marrow stem cells, marrow transplants remain incredibly hard on a patient.

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Now, engineers at the University of California San Diego have developed a synthetic bone implant with functional marrow able to produce its own blood cells. So far, researchers revealed in a paper published in the Proceedings of the National Academy of Sciencesthis week, they have successfully tested the engineered bone tissues in mice. But one day, those biomimetic bone tissues could provide new bone marrow for human patients in need of transplants, too.

The implant does away with the need for radiation by giving donor cells their own space in the body to grow. Inside the implant, there is no threat of those cells being overtaken by the body’s native stem cells.

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In mice, the researchers implanted the synthetic bone tissues with functional marrow under the skin. After six months, those donor cells were still alive and had begun supplying the mice with new blood cells.

The implants were designed to replicate the long bones in the body, with an outer bone compartment containing calcium phosphate minerals to build bone cells, and an inner area for donor stem cells that produce blood cells.

When implanted, they grew into bone tissues with working blood vessel network and functional bone marrow that supplied the body new blood cells. After 24 weeks, researchers found a mix of host and donor blood cells was still circulating in the bloodstream of the mice.

A treatment based on this technology would only work for patients with non-malignant bone marrow diseases, like aplastic anemia, a condition where the body can’t make enough platelets and blood cells. That’s because while the technique can replenish types of cells that are lacking, it can’t doing anything to fight off cells that have mutated and are spreading. Cancer patients would still need need to undergo radiation therapy to have their cancerous cells wiped out.

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Much more research is needed, of course, before these implants are ready to make their way into human patients. But what’s exciting here is that the synthetic bone tissues were not only functional, they allowed donor marrow to grow and survive for many weeks in the presence of host cells, and for the products of that marrow to make their way into the body’s circulatory system. Pretty neat.